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1 <html>
2 <head>
3 <title>pcreprecompile specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreprecompile man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
17 <li><a name="TOC2" href="#SEC2">SAVING A COMPILED PATTERN</a>
18 <li><a name="TOC3" href="#SEC3">RE-USING A PRECOMPILED PATTERN</a>
20 <li><a name="TOC5" href="#SEC5">AUTHOR</a>
21 <li><a name="TOC6" href="#SEC6">REVISION</a>
22 </ul>
24 <P>
25 If you are running an application that uses a large number of regular
26 expression patterns, it may be useful to store them in a precompiled form
27 instead of having to compile them every time the application is run.
28 If you are not using any private character tables (see the
29 <a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
30 documentation), this is relatively straightforward. If you are using private
31 tables, it is a little bit more complicated. However, if you are using the
32 just-in-time optimization feature, it is not possible to save and reload the
33 JIT data.
34 </P>
35 <P>
36 If you save compiled patterns to a file, you can copy them to a different host
37 and run them there. If the two hosts have different endianness (byte order),
38 you should run the <b>pcre[16|32]_pattern_to_host_byte_order()</b> function on the
39 new host before trying to match the pattern. The matching functions return
40 PCRE_ERROR_BADENDIANNESS if they detect a pattern with the wrong endianness.
41 </P>
42 <P>
43 Compiling regular expressions with one version of PCRE for use with a different
44 version is not guaranteed to work and may cause crashes, and saving and
45 restoring a compiled pattern loses any JIT optimization data.
46 </P>
47 <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
48 <P>
49 The value returned by <b>pcre[16|32]_compile()</b> points to a single block of
50 memory that holds the compiled pattern and associated data. You can find the
51 length of this block in bytes by calling <b>pcre[16|32]_fullinfo()</b> with an
52 argument of PCRE_INFO_SIZE. You can then save the data in any appropriate
53 manner. Here is sample code for the 8-bit library that compiles a pattern and
54 writes it to a file. It assumes that the variable <i>fd</i> refers to a file
55 that is open for output:
56 <pre>
57 int erroroffset, rc, size;
58 char *error;
59 pcre *re;
61 re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
62 if (re == NULL) { ... handle errors ... }
63 rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
64 if (rc &#60; 0) { ... handle errors ... }
65 rc = fwrite(re, 1, size, fd);
66 if (rc != size) { ... handle errors ... }
67 </pre>
68 In this example, the bytes that comprise the compiled pattern are copied
69 exactly. Note that this is binary data that may contain any of the 256 possible
70 byte values. On systems that make a distinction between binary and non-binary
71 data, be sure that the file is opened for binary output.
72 </P>
73 <P>
74 If you want to write more than one pattern to a file, you will have to devise a
75 way of separating them. For binary data, preceding each pattern with its length
76 is probably the most straightforward approach. Another possibility is to write
77 out the data in hexadecimal instead of binary, one pattern to a line.
78 </P>
79 <P>
80 Saving compiled patterns in a file is only one possible way of storing them for
81 later use. They could equally well be saved in a database, or in the memory of
82 some daemon process that passes them via sockets to the processes that want
83 them.
84 </P>
85 <P>
86 If the pattern has been studied, it is also possible to save the normal study
87 data in a similar way to the compiled pattern itself. However, if the
88 PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is created cannot
89 be saved because it is too dependent on the current environment. When studying
90 generates additional information, <b>pcre[16|32]_study()</b> returns a pointer to a
91 <b>pcre[16|32]_extra</b> data block. Its format is defined in the
92 <a href="pcreapi.html#extradata">section on matching a pattern</a>
93 in the
94 <a href="pcreapi.html"><b>pcreapi</b></a>
95 documentation. The <i>study_data</i> field points to the binary study data, and
96 this is what you must save (not the <b>pcre[16|32]_extra</b> block itself). The
97 length of the study data can be obtained by calling <b>pcre[16|32]_fullinfo()</b>
98 with an argument of PCRE_INFO_STUDYSIZE. Remember to check that
99 <b>pcre[16|32]_study()</b> did return a non-NULL value before trying to save the
100 study data.
101 </P>
102 <br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
103 <P>
104 Re-using a precompiled pattern is straightforward. Having reloaded it into main
105 memory, called <b>pcre[16|32]_pattern_to_host_byte_order()</b> if necessary, you
106 pass its pointer to <b>pcre[16|32]_exec()</b> or <b>pcre[16|32]_dfa_exec()</b> in
107 the usual way.
108 </P>
109 <P>
110 However, if you passed a pointer to custom character tables when the pattern
111 was compiled (the <i>tableptr</i> argument of <b>pcre[16|32]_compile()</b>), you
112 must now pass a similar pointer to <b>pcre[16|32]_exec()</b> or
113 <b>pcre[16|32]_dfa_exec()</b>, because the value saved with the compiled pattern
114 will obviously be nonsense. A field in a <b>pcre[16|32]_extra()</b> block is used
115 to pass this data, as described in the
116 <a href="pcreapi.html#extradata">section on matching a pattern</a>
117 in the
118 <a href="pcreapi.html"><b>pcreapi</b></a>
119 documentation.
120 </P>
121 <P>
122 <b>Warning:</b> The tables that <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> use
123 must be the same as those that were used when the pattern was compiled. If this
124 is not the case, the behaviour is undefined.
125 </P>
126 <P>
127 If you did not provide custom character tables when the pattern was compiled,
128 the pointer in the compiled pattern is NULL, which causes the matching
129 functions to use PCRE's internal tables. Thus, you do not need to take any
130 special action at run time in this case.
131 </P>
132 <P>
133 If you saved study data with the compiled pattern, you need to create your own
134 <b>pcre[16|32]_extra</b> data block and set the <i>study_data</i> field to point
135 to the reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in
136 the <i>flags</i> field to indicate that study data is present. Then pass the
137 <b>pcre[16|32]_extra</b> block to the matching function in the usual way. If the
138 pattern was studied for just-in-time optimization, that data cannot be saved,
139 and so is lost by a save/restore cycle.
140 </P>
142 <P>
143 In general, it is safest to recompile all saved patterns when you update to a
144 new PCRE release, though not all updates actually require this.
145 </P>
146 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
147 <P>
148 Philip Hazel
149 <br>
150 University Computing Service
151 <br>
152 Cambridge CB2 3QH, England.
153 <br>
154 </P>
155 <br><a name="SEC6" href="#TOC1">REVISION</a><br>
156 <P>
157 Last updated: 12 November 2013
158 <br>
159 Copyright &copy; 1997-2013 University of Cambridge.
160 <br>
161 <p>
162 Return to the <a href="index.html">PCRE index page</a>.
163 </p>


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